Bainite steel and methods of manufacture thereof

Abstract

Super Bainite Steel is described comprising between 90 % and 50 % bainite, the rest being austenite, in which excess carbon remains within the bainitic ferrite at a concentration beyond that consistent with equilibrium; there is also partial partitioning of carbon into the residual austenite. Such bainite steel has very fine bainite platelets (thickness 100nm or less). In this specification the expression 'Super Bainite Steel' is used for such steel. In particular, the impact of varying the manganese content to achieve fast transformation times, and hence low manufacturing costs without the presence of expensive alloying materials is discussed. In one embodiment of the invention a Super Bainite Steel comprises in weight percent: carbon 0.6 to 1.1 %, silicon 1.5 to 2.0 %, manganese 0.5 to 1.8 %, nickel up to 3 %, chromium 1.0 to 1.5 %, molybdenum 0.2 to 0.5 %, vanadium 0.1 to 0.2 %, balance iron save for incidental impurities. In particular it was noted that excellent properties were obtained if the manganese content is about 1% by weight. Various processes for making the Super Bainite Steel are discussed, but a particularly useful process includes the step of cooling the steel from an austenite quickly enough to avoid transformation to pearlite and transforming the steel to bainite at a temperature in the range 190 DEG C to 2500 DEG C. The patent discusses the impact of changing the transition temperature on hardness, and conclude that the invention can provide a very hard steel (>630HV). It is also noted that suitable pearlite can be produced for cutting drilling and shaping, before final transformation to Super Bainite Steel.

Description

technical field [0001] The present invention relates to bainitic steel and a method for its manufacture. The invention, although particularly concerned with steels suitable for use as armor, is not limited to such steels. The invention also relates to transition microstructures which can subsequently be processed into bainitic steels. Background technique [0002] Predominantly bainitic steels are generally steels with a ferritic structure of at least 50% bainite. Bainite is divided into two types: upper bainite and lower bainite. [0003] Upper bainite does not contain carbide precipitates within the bainitic ferrite grains, but may have precipitated carbides at grain boundaries. [0004] Lower bainite has precipitated carbides inside bainitic ferrite grains forming characteristic angles with grain boundaries. Precipitated carbides can also be present at the grain boundaries. [0005] Carbide-free bainite has recently been described, which consists of 90% to 50% bainit...

AI Technical Summary

Problems solved by technology

Although this material has a lower alloy cost compared to other known hard armor steels, fabrication involves prolonged heating, especially in the transformation to bainite, resulting in higher energy costs and longer production times

It is also extremely difficult to machine, hole and form this bainitic steel

Therefore, its industrial application is limited

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